Television and Home Theater

Having a intermitent problem, first in eight years. After a few hours of viewing, screen goes dark except for a bright horizontal line in the center of the TV. After shutting it off, picture returns but repeats with the horizontal line. Other than that, the picture is still sharp, bright colors and sound. Any ideas?

Hello: I have a 4 year old Philips 32PT71B (32"). It has given me no problems until after a power outage about 2 weeks ago. Now, the TV volume meter shows up on its own will occasionally dial down, but usually dials up to the loudest setting, even with the batteries removed from both the TV and cable remotes. When the volume would rise, I'd hold down the volume on both remotes so as to not wake up my neighbors! The same thing happens with the brightness. To turn off the TV, I have to turn off the surge protector or unplug the TV from the wall. Otherwise, it'd keep turning on on its own.

I have a (2000)panosonic ct 27D10B TV it has lines at the top of the screen but the picture itself is great!
It used to go away after a minute, but now it's constant! any ideas what causes it?
Thanx for any info!